1. Field of the Invention
This invention relates to a brake fluid pressure control apparatus for a vehicle which controls braking slip and driving slip of wheels.
2. Description of the Prior Arts:
For example, the West German Patent Opening Gazette No.2139230 and the Japanese Patent Application No. 221530/1988 disclose the brake fluid pressure control apparatus for a vehicle in which a fluid pressure control valve is arranged in a conduit connecting a master cylinder with a wheel cylinder for controlling the brake fluid pressure of the wheel, and further a cut-off valve is arranged between the fluid pressure control valve and the master cylinder. The cut-off valve is open during the normal operation and during the anti-skid control operation. It is closed during the drive slip control operation in which the brake pressure is so increased, decreased and maintained at constant by the control of the fluid pressure control valve that the driven wheel rotates at the optimum slip.
However, when the driver treads the brake pedal during the drive slip control operation, the brake pressure is transmitted to the wheel cylinder in some time lag. The brake light switch requires some time to detect the tread of the brake pedal. The control unit requires some time to judge that the drive slip control has become necessary no longer. The fluid pressrue control valve requires some time to change over to the initial position, in which the master cylinder and the wheel cylinder communicate with each other, from the other position to decrease the brake pressure or maintain it, if the fluid pressure control valve is changed over to the other position during the drive slip control operation. The above required times are totalled to the above time lag. Thus, it is difficult to rapidly brake the vehicle of the driver's free will during the drive slip control operation.